Ever since invented, carbon materials such as conductive carbon have been attracting attention due to their high electrical conductivity and heat conductivity. Above all, sheet-like structures made solely of carbon materials are, due to their characteristics, expected to open up a variety of application possibilities, such as in storage devices.
In recent years, carbon nanotubes (hereinafter, may be called “CNTs”) are especially becoming the center of attention as a material having excellent electrical conductivity, heat conductivity, and mechanical characteristics.
However, CNTs are fibrous carbon nanostructures having a nanometer-sized diameter, which makes handling and processing of individual CNTs difficult. In consideration of this, a plurality of CNTs may be aggregated into a film shape to form a carbon nanotube film (hereinafter, may be called a “CNT film”), which is sometimes also referred to as a “buckypaper”. Thus formed CNT film is proposed to be used, for example, as a conductive film. More concretely, it has been proposed that a CNT film may be used as a component (e.g., a conductive film or a cathode catalyst layer) of an electrode included in a solar cell, a touch panel, or the like (refer, for example, to Patent Literature 1). The proposed CNT film is formed by removing a solvent from a CNT dispersion liquid containing the solvent and CNTs, by way of filtration, drying, or other methods.